This invention relates to drop on demand ink jet printing apparatus and, in one example, to drop on demand ink jet printing apparatus having a two dimensional array of ink chambers.
Drop on demand ink jet printing apparatus, particularly inkjet printheads, typically comprise a chamber supplied with droplet fluid and communicating with a nozzle for ejection of droplets therefrom, and means actuable by electrical signals to vary the volume of the chamber, the volume variation being sufficient to effect droplet ejection.
However, with such arrangements there remains problems associated with providing a high density two dimensional array of ink chambers operable at high frequency and with low manufacturing costs.
The present invention seeks to solve these and other problems.
Accordingly, it is an object of at least the preferred embodiments of the present invention to provide ink jet printing apparatus that is capable of both high performance and efficiency coupled with a simple manufacturing method and low cost that can be manufactured into a two dimensional array.
It is another such object to allow simpler methods of electrical interconnect and a wider choice of electrical interconnect methods within a shear mode drop on demand ink jet printing apparatus.
It is another such object to allow a configuration of a roof mode shear disc actuator that does not suffer from the constraints of cross talk between neighbouring actuators.
It is another such object to allow for the capability of a large matrix shear mode array to be manufactured from a number of smaller matrices.
In a first aspect, the present invention provides drop-on-demand ink jet printing apparatus, comprising a nozzle on a nozzle axis; an ink chamber extending radially about the nozzle axis; ink supply means communicating with the ink chamber and an actuator movable in the direction of the nozzle axis to effect, through acoustic wave travel in the ink chamber radially of the nozzle axis, ejection of an ink drop through the nozzle and replenishment of the ink chamber with ink.
In one preferred embodiment, the ink chamber extends a radial distance R from the nozzle axis, the actuator being movable in the direction of the nozzle between first and second configurations in a time which is at least half of the time R/c, where c is the speed of sound through ink in the ink chamber. For example, with the ink chamber extending a radial distance of 0.5 mm and with the speed of sound through ink in the ink chamber being 500 m/s, the nozzle is moveable between configurations in a time which is at most 500 ns. Preferably, the nozzle is moveable between configurations in a time which is at least an order of magnitude less than the time R/c, more preferably of an order of nanoseconds.
In a preferred embodiment, the actuator comprises a piezoelectric actuating disc associated with the ink chamber and moveable to or from a domed configuration to effect ink drop ejection, the apparatus further comprising electrodes for applying an actuating electric field to the piezoelectric disc.
Preferably, the piezoelectric disc is homogeneous and so poled in relation to the actuating electric field as to move in shear mode. If so, the electric field may be applied in the direction of the nozzle axis, the piezoelectric disc being poled radially.
The piezoelectric disc may be poled in directions which all converge towards the nozzle axis.
The electrodes may comprise a ground electrode on a face of the piezoelectric disc abutting the ink chamber and another electrode on an opposing face of the piezoelectric disc.
The disc may be provided with a projecting member projecting along the nozzle axis, or with a recess substantially concentric with the nozzle.
The ink supply means may serve to supply ink to the ink chamber in a direction radially of the nozzle axis.
The ink supply means may serve to supply ink to the ink chamber at a plurality of locations disposed circumferentially about the ink chamber, preferably serving to supply ink to the ink chamber around substantially the entire periphery of the ink chamber.
The ink chamber may be bounded by a generally circular structure providing a change in acoustic impedance serving to reflect acoustic waves travelling in the ink chamber radially of the nozzle axis. This change in acoustic impedance may be effected through a change in ink depth in the direction of the nozzle axis. The structure may define an annulus of ink about the ink chamber which in the direction of the nozzle axis is of a depth different from the depth of the ink chamber. This annulus may form part of the ink supply means.
Preferably, the apparatus comprises a plurality of said nozzles, each having a respective nozzle axis, said nozzles being provided in parallel and in a two dimensional planar array; a plurality of said ink chambers, each extending about a respective nozzle axis; and a homogeneous piezoelectric sheet having a two dimensional array of said actuators, each actuator being associated with a respective ink chamber.
With such an arrangement, the apparatus may comprise a plurality of said electrodes, one common ground electrode on a face of the piezoelectric sheet abutting the ink chambers and on an opposing face, individual electrodes associated respectively with the ink chambers. The individual electrodes may be connected to electrical pulse applying means through respective electrical connections provided on an interconnection plate laminated with the nozzle plate and the piezoelectric sheet.
The nozzles may be formed in a nozzle plate, said nozzle plate being laminated with the piezoelectric sheet to provide said plurality of ink chambers.
The ink supply means may comprise an array of ink channels formed in said piezoelectric sheet, and ink transfer means for transferring ink from the ink channels to the ink chambers. The ink transfer means may comprise an array of recesses formed in an intermediate plate laminated with the nozzle plate and the piezoelectric sheet.
The nozzle plate, interconnection plate and intermediate plate may each comprise a piezoelectric sheet. Alternatively, the nozzle plate, interconnection plate and intermediate plate may each comprise a sheet of material thermally compatible with the piezoelectric sheet.
In a second aspect, the present invention provides drop-on-demand ink jet printing apparatus comprising a nozzle; an ink chamber communicating with the nozzle; a piezoelectric actuating disc associated with the ink chamber and movable to or from a generally domed configuration to effect droplet ejection through the nozzle; and electrodes for applying an actuating electric field to the piezoelectric disc, wherein the piezoelectric disc is homogeneous and so poled in relation to the actuating electric field as to move in shear mode.
The apparatus may further comprise ink supply means communicating with the ink chamber for replenishment of the ink chamber with ink following droplet ejection.
Preferably, the ink chamber extends radially about the axis of the nozzle, and the disc is moveable to effect, through acoustic wave travel in the ink chamber radially of the axis of the nozzle, droplet deposition through the nozzle.
In a third aspect, the present invention provides drop-on-demand ink jet printing apparatus comprising a two dimensional planar array of parallel nozzles each having a nozzle axis; a plurality of disc-shaped ink chambers each extending about a respective nozzle axis and communicating with the respective nozzle; a homogeneous piezoelectric sheet having a two dimensional array of circularly symmetric actuating regions associated respectively with the ink chambers; and electrodes on the piezoelectric sheet enabling selective actuation of each region thereby to eject a droplet from the associated nozzle.
In a fourth aspect, the present invention provides a method of ink jet printing comprising the steps of establishing a planar body of ink in communication with a nozzle having a nozzle axis, the body of ink extending radially of the nozzle axis; providing in the body of ink an impedance boundary extending circumferentially of the nozzle axis; and selectively moving an actuator in the direction of the nozzle axis so as to establish an acoustic wave travelling radially of the nozzle axis in the ink chamber and reflected by the impedance boundary, thereby to effect ejection of an ink droplet through the nozzle.
The method may further comprise the step of replenishing the body of ink following ink droplet ejection by supplying ink thereto in a direction radial of the nozzle axis.
In a fifth embodiment, the present invention provides a method of manufacturing drop-on-demand ink jet printing apparatus, comprising the steps of forming a nozzle plate having a two dimensional planar array of parallel nozzles each having a nozzle axis; forming a homogeneous piezoelectric sheet having a two dimensional array of circularly symmetric actuating regions associated respectively with the nozzles; applying electrodes on the piezoelectric sheet enabling selective actuation of each region; and laminating the nozzle plate and the piezoelectric sheet, the laminated structure providing a plurality of disc-shaped ink chambers each extending about a respective nozzle axis and communicating with the respective nozzle, such that in the manufactured apparatus, actuation of a selected region of the piezoelectric sheet effects drop ejection from the associated nozzle.
The plurality of ink chambers may be provided by a two dimensional array of circularly symmetric recesses formed in said piezoelectric sheet, each actuating region comprising at least part of the bottom wall of a respective circularly symmetric recess.
The circularly symmetric recesses may be formed by removal of material from the piezoelectric sheet, or during moulding of the piezoelectric sheet.
Polarised actuating regions may be formed by the steps of forming a resist layer on each side of said piezoelectric sheet, exposing the outer side walls and the central portion of the inner bottom wall of each circularly symmetric recess, developing said resist layers, forming a metallic layer on each side of piezoelectric sheet to cover the exposed regions of each circularly symmetric recess, and applying an electric field across said metallic layers.
Electrodes may be formed by the steps of subsequently removing said developed resist layers and said metallic layers, forming resist layers on respective faces of each polarised actuating region, developing said resist layers, forming an electrically insulating layer on both sides of the piezoelectric sheet, removing said resist layers to expose both faces of each polarised actuating region, and depositing said electrodes on both faces of each polarised actuating regions for effecting deflection of the actuating regions in shear mode in the direction of the electric field applied by the electrodes.
Electrical connections to individual electrodes may be formed on an interconnection plate mounted on said piezoelectric sheet. Holes may be formed in the interconnection plate, electrical connections passing through the holes for connection to respective individual electrodes.
An array of ink channels may be formed in the piezoelectric sheet for supplying ink to the ink chambers. The array of ink channels may be formed in the same side of the piezoelectric sheet as the array of circularly symmetric recesses, ink transfer means being provided for transferring ink from the ink channels to the ink chambers.